1. Field
The present disclosure relates generally to position or location estimations of mobile communication devices and, more particularly, to improved E911 positioning via background signal tracking for use in or with mobile communication devices.
2. Information
Mobile communication devices, such as, for example, cellular telephones, portable navigation units, laptop computers, personal digital assistants, or the like are becoming more common every day. Certain mobile communication devices, such as, for example, location-aware cellular telephones, smart telephones, or the like may assist users in estimating their geographic locations by providing positioning assistance parameters obtained or gathered from various systems. For example, in an outdoor environment, certain mobile communication devices may obtain an estimate of their geographic location or so-called “position fix” by acquiring wireless signals from a satellite positioning system (SPS), such as the global positioning system (GPS) or other like Global Navigation Satellite Systems (GNSS), cellular base station, etc. via a cellular telephone or other wireless or electronic communications network. Acquired wireless signals may, for example, be processed by or at a mobile communication device, and its location may be estimated using known techniques, such as Advanced Forward Link Trilateration (AFLT), base station identification, cell tower triangulation, or the like.
In an indoor or like environment, such as urban canyons, for example, mobile communication devices may be unable to reliably receive or acquire satellite or like wireless signals to facilitate or support one or more position estimation techniques. For example, signals from an SPS or other wireless transmitters may be attenuated or otherwise affected in some manner (e.g., insufficient, weak, fragmentary, etc.), which may at least partially preclude their use for position estimations. At times, a mobile communication device may obtain a position fix by measuring ranges to three or more terrestrial wireless transmitter devices, such as cellular base stations, access points, etc. positioned at known locations. Ranges may be measured, for example, by obtaining a Media Access Control identifier (MAC ID) address from wireless signals received from suitable access points and measuring one or more characteristics of received signals, such as signal strength, round trip delay, or the like.
In some instances, a position fix of a mobile communication device may be obtained in connection with an observed time difference of arrival (OTDOA) technique. In this technique, a mobile communication device may measure timing differences between reference signals received from two or more pairs of cellular base stations, for example, and may obtain a position fix based, at least in part, on known locations and transmission timing for the measured base stations. An OTDOA positioning technique may, for example, be employed to assist in localization of a mobile communication device in the event of an emergency call, such as in compliance with Emergency 911 (E911) mandates from the Federal Communication Commission (FCC). At times, however, OTDOA positioning accuracy may be affected, at least in part, by receiver sensitivity or hearability issues, such as if wireless signals of OTDOA requests acquired from proximate cellular base stations have low or insufficient power, such as to facilitate or support appropriate measurements (e.g., reference signal time differences, etc.), for example. In some instances, OTDOA positioning accuracy may also be affected, at least in part, by signal multipath or scattering effects, for example, which may introduce errors to observed arrival times of OTDOA reference signals. E911 OTDOA positioning may also rely or, at times, be dependent on a dedicated positioning architecture, such as having a dedicated location server, for example, to manage OTDOA positioning by providing assistance data (e.g., OTDOA requests, reference signals, etc.) to mobile communication devices and computing a location estimate.